The present invention relates generally to fluorescent illuminating devices, and, more particularly, to an inductive-resistive fluorescent apparatus and method.
Fluorescent lamps are well known in the prior art. There are three basic types of such lamps. These are the preheat lamp, the instant-start lamp, and the rapid-start lamp. In each type of lamp, a glass tube is provided which has a coating of phosphor powder on the inside of the tube. Electrodes are disposed at opposite ends of the tube. The tube is filled with an inert gas, such as argon, and a small amount of mercury. Electrons emitted from the electrodes strike mercury atoms contained within the tube, causing the mercury atoms to emit ultraviolet radiation. The ultraviolet radiation is absorbed by the phosphor powder, which in turn emits visible light via a fluorescent process.
The differences between the three lamp types generally relate to the manner in which the lamp is initially started. Referring now to FIG. 1, in a preheat lamp circuit, designated generally as 10, a starter bulb 12 is included. Preheat lamp 14 includes first and second electrodes 16 and 18, each of which has two terminals 20. During initial start-up of the preheat lamp, starter bulb 12, which acts as a switch, is closed, thus shorting electrodes 16 and 18 together. Current therefore passes through electrode 16 and then through electrode 18. This current serves to preheat the electrodes, making them more susceptible to emission of electrons. After a suitable time period has elapsed, during which the electrodes 16 and 18 have warmed up, the starter bulb 12 opens, and thus, an electric potential is now applied between electrodes 16 and 18, resulting in electron emission between the two electrodes, with subsequent operation of the lamp.
A relatively high voltage is applied initially for starting purposes. A lower voltage is used during normal operation. A reactance is placed in series with the lamp to absorb any difference between the applied and operating voltages, in order to prevent damage to the lamp. The reactance, suitable transformers, capacitors, and other required starting and operating components are contained within a device known as a ballast (designated generally as 22). Ballasts are relatively large, heavy and expensive, with inherent efficiency limitations and difficulties in operating at low temperatures. The components within ballasts are typically potted with a thermally conductive, electrically insulating compound, in an effort to dissipate the heat generated by the components of the ballast. Difficulties in heat dissipation are yet another disadvantage of conventional ballasts.
Referring now to FIG. 2, an instant-start lamp circuit, designated generally as 24, is shown. Instant-start lamp 26 includes first and second electrodes 28 and 30.
Electrodes 28 and 30 each only have a single terminal designated as 32. In operation of the instant-start lamp, no preheating of the electrodes is required. Rather, an extremely high starting voltage is typically applied in order to induce current flow without preheating of the electrodes. The high starting voltage is supplied by a special instant-start ballast, designated generally as 34. Instant-start type ballasts suffer from similar disadvantages to those of the preheat type. Further, because of the danger of the high starting voltage from the instant-start ballast 34, a special disconnect lamp holder 36 must be employed in order to disconnect the ballast when the lamp 26 is not properly secured in position.
Referring now to FIG. 3, a rapid-start lamp circuit, designated generally as 38, is shown. Rapid start lamp 40 includes first and second electrodes 42 and 44, each of which has two terminals 46, similar to the preheat lamp 14, discussed above. The rapid-start ballast, designated generally as 48, contains transformer windings, which continuously provide the appropriate voltage and current for heating of the electrodes 42 and 44. Rapid heating of electrodes 42 and 44 permits relatively fast development of an arc from electrode 42 to electrode 44 using only the applied voltage from the secondary windings present in ballast 48. The rapid start ballast 48 permits relatively quick lamp starting, with smaller ballasts than those required for instant-start lamps, and without flicker which may be associated with preheat lamps. Further, no starter bulb is required. However, ballast 48 is still relatively large, heavy, inefficient, and unsuitable to low ambient-temperature operation. Dimming and flashing of rapid-start lamps are possible, albeit with the use of special ballasts and circuits.
It will be appreciated that operation of the prior art lamps described above is dependent on heating of the electrodes and/or application of a high voltage between the electrodes in order to start the operation of the lamp. This necessitates the use of ballasts and associated control circuitry, having the undesirable attributes discussed above. Recently, there has been interest in employing other physical phenomena to enable efficient starting and operation of fluorescent lamps. For example, EPO Publication Number 0 593 312 A2 discloses a fluorescent light source illuminated by means of an RF (radio frequency) electromagnetic field. However, the device of the ""312 publication still suffers from numerous disadvantages, including the complex circuitry required to generate the RF field and the potential for RF interference.
In the parent international Application No. PCT/US97/18650, a ballast-free drive circuit is disclosed which, in one embodiment, employs a direct current (DC) or pulsed DC source (see FIG. 25). It has been found, however, that operating a fluorescent lamp with a DC or pulsed DC source can lead to mercury migration in the lamp and an associated reduction of light output over time. This mercury migration problem may, therefore, substantially shorten the usable life of the fluorescent lamp.
Through experimentation, it was additionally observed that the fluorescent lamp drive circuit disclosed in the parent International Application exhibited unreliable starting of the fluorescent lamp, particularly when used with certain types of fluorescent lamps (e.g., T8 lamps). This starting problem was found to be related, at least in part, to an insufficient voltage being generated across the output capacitors in the drive circuit. In such instances, the capacitors were not always fully charged to an appropriate voltage level necessary to form the arc in the fluorescent medium.
There is, therefore, a need in the prior art for an inductive-resistive fluorescent apparatus which permits simple, economical and reliable starting and operation of fluorescent lamps with low-cost, light weight, low-volume components which are capable of efficiently operating the lamp, even at relatively low ambient temperatures, which afford efficient heat dissipation and which are capable of operating at ordinary household AC frequencies. It is desirable to adapt such an inductive-resistive fluorescent apparatus to substantially eliminate mercury migration in the fluorescent lamp. It is additionally desirable to provide a fluorescent apparatus having the flexibility for enhanced features, including the ability to remotely control the fluorescent apparatus via a proportional industrial controller (PIC) or similar building controller. Furthermore, it is desirable to adapt such an inductive-resistive apparatus to direct xe2x80x9cplug-inxe2x80x9d replacement of incandescent bulbs.
The present invention, which addresses the needs of the prior art, provides an inductive-resistive fluorescent apparatus and method. The apparatus includes a translucent housing having a chamber for supporting a fluorescent medium, and having electrical connections configured to provide an electrical potential across the chamber. A fluorescent medium is supported within the chamber. An inductive-resistive structure is fixed sufficiently proximate to the housing in order to induce fluorescence in the fluorescent medium when an electric current is passed through the inductive-resistive structure, while an electric potential is applied across the housing. In a preferred embodiment, the translucent housing and fluorescent medium are contained as part of a conventional fluorescent lightbulb.
In one aspect, the present invention includes a fluorescent illuminating apparatus comprising a fluorescent lightbulb; an inductive-resistive structure; and a source of rippled/pulsed direct current. The fluorescent lightbulb includes a translucent housing with a chamber for supporting a fluorescent medium; electrical connections on the housing to provide an electrical potential across the chamber; a fluorescent medium supported in the chamber; and first and second electrodes at first and second ends of the translucent housing, which are electrically interconnected with the first and second electrical terminals. The inductive-resistive structure is fixed sufficiently proximate to the housing of the lightbulb to induce fluorescence in the fluorescent medium when an electric current is passed through the inductive-resistive structure while an electric potential is applied across the housing. The inductive-resistive structure has third and fourth electrical terminals. The second and third electrical terminals are electrically interconnected.
The source of rippled/pulsed direct current has first and second output terminals interconnected with the first and fourth electrical terminals and has first and second alternating current input terminals. The source includes a first diode having its anode electrically interconnected with the second output terminal and its cathode electrically interconnected with the first AC input terminal; a second diode with its anode electrically interconnected with the first AC input terminal and its cathode electrically interconnected with the first output terminal; a third diode having its anode electrically interconnected with the second AC input terminal and having its cathode electrically interconnected with the first output terminal; a fourth diode having its anode electrically interconnected with the second output terminal and its cathode electrically interconnected with the second AC input terminal; a first capacitor electrically interconnected between the first output terminal and the second AC input terminal; and a second capacitor electrically interconnected between the second output terminal and the second AC input terminal.
In another aspect a fluorescent illuminating apparatus includes a fluorescent lightbulb as in the first aspect. The apparatus further includes an inductive-resistive structure fixed sufficiently proximate to the housing of the lightbulb to induce fluorescence in the fluorescent medium when an electric current is passed through the inductive-resistive structure while an electric potential is applied across the housing. The inductive-resistive structure has third and fourth electrical terminals. In the second aspect, the apparatus further includes a source of rippled/pulsed direct current including a first transistor; a first capacitor; and a step-up transformer. The step-up transformer has a primary and a secondary winding with the secondary winding electrically interconnected to the first and second electrical terminals of the fluorescent lightbulb and the primary winding electrically interconnected with the first transistor, the first capacitor and the inductive-resistive structure to form an oscillator, such that when a source of substantially steady direct current is electrically interconnected with the oscillator, the first capacitor charges during a first repeating time period when the first transistor is off and the first capacitor discharges during a second repeating time period when the first transistor is active. The oscillator produces a time-varying voltage waveform across the primary winding of the transformer in accordance with the charging and discharging of the first capacitor during the first and second repeating time periods, such that a stepped-up rippled/pulsed direct current is produced in the secondary winding. A source of substantially steady direct current (DC voltage), such as a storage battery, can be electrically interconnected with the oscillator.
In yet another aspect of the present invention, a fluorescent illuminating apparatus includes a translucent housing having a chamber for supporting a fluorescent medium and having electrical connections thereon to provide an electrical potential across the chamber. The housing generally has the size and shape of an ordinary incandescent lightbulb, and the electrical connections are in the form of first and second electrical terminals adapted to mount into an ordinary light socket. The apparatus further includes a fluorescent medium supported in the chamber and first and second spaced electrodes located within the chamber. Yet further, a first inductive-resistive structure is included, preferably located within the chamber, and a source of rippled/pulsed direct current (DC voltage) is included which has first and second alternating current input terminals electrically interconnected with the first and second electrical terminals. The source also has first and second output terminals. The first electrode is electrically interconnected with the first output terminal and the second electrode is electrically interconnected with the second output terminal through the first inductive-resistive structure.
In still another aspect of the present invention, the source of rippled/pulsed direct current is converted to a low-frequency alternating current (AC) drive source. The AC drive source preferably includes an H-bridge circuit and an associated controller. The H-bridge circuit in combination with the controller performs a polarity reversing function, thereby substantially eliminating the mercury migration problem of the prior art. In addition to periodically reversing the polarity of the fluorescent lamp current, the controller preferably controls and maintains a lamp current having a predefined duty cycle, thereby providing enhanced dimming capabilities for the fluorescent lamp in accordance with the apparatus and method of the present invention.
A preferred method of the present invention includes delaying the presentation of the drive source voltage to the fluorescent lamp for a predetermined amount of time so as to enable the output capacitors in the voltage multiplier circuit to fully charge, thereby substantially eliminating the starting problems which exist in prior art fluorescent apparatus. The method further preferably includes measuring the current passing through the fluorescent lamp and providing a control circuit, whereby the duty cycle of the lamp current, and therefore the lamp brightness, can be variably adjusted by the user in predetermined increments.
Any of the apparatuses of the present invention can be configured with a spike delay trigger or voltage sensing trigger to enhance starting at low voltage, and can include a fluorescent bulb having an inductive-resistive strip mounted therein. The inductive-resistive structures can include first and second spaced (preferably elongate) conductors, with a conductive-resistive medium electrically interconnected between the conductors. The conductive-resistive medium may be, for example, a solid emulsion consisting of an electrically conductive discrete phase dispersed within a non-conductive continuous phase. A preferred emulsion includes powdered graphite and an alkali silicate (such as china clay) dispersed in a polymeric binder. The medium may also be a coating portion of a magnetic recording tape. One or more discrete resistors can also be employed.
The conductive-resistive medium may be located on a separate substrate, or a may be applied to the surface of the fluorescent lightbulb itself. Further, the inductive-resistive structure may be positioned in thermal communication with the translucent housing in order to aid in low-temperature operation of the inductive-resistive fluorescent apparatus, by means of transferring ohmic heat from the inductive-resistive structure to the translucent housing. (Even when there is no such heat transfer, the present invention provides better low-temperature operation than a conventional ballast.) It is believed that the inductive-resistive structure of the invention assists in starting and operation of the fluorescent lightbulb by means of an electromagnetic (e.g., magnetic and/or electrostatic) field interaction.
Another method of the present invention includes passing a current through an inductive-resistive structure, which is adjacent, a fluorescing medium, in an amount sufficient to induce fluorescence in the presence of an electric potential imposed on the fluorescing medium. Preferably, the inductive-resistive structure comprises a conductive-resistive medium electrically interconnected between first and second spaced (most preferably elongate) conductors. The conductive-resistive medium is preferably maintained within about one inch (2.5 cm) or less of the fluorescing medium, at least for starting purposes, in order to maximize the electromagnetic field interaction between the inductive-resistive structure and the fluorescing medium. In alternative embodiments discussed herein, the inductive-resistive structure may be maintained at a greater distance from the fluorescing medium.
Various types of conductive-resistive media are described in detail in Applicants"" U.S. Pat. Nos. 4,758,815; 4,823,106; 5,180,900; 5,385,785; and 5,494,610. The disclosures of all of the foregoing patents are incorporated herein by reference. Specific details regarding preferred media for use with the present invention are given herein.
As a result of the foregoing, the present invention provides an inductive-resistive fluorescent apparatus offering relatively low Weight, low volume, simplicity and low cost compared to prior ballast-operated systems. The apparatus is capable of low-ambient-temperature operation, which may be enhanced by configuring the inductive apparatus to generate ohmic heat and transfer at least a portion of the heat into the fluorescent lamp. Inductive structures which are relatively thin and which have a relatively large surface area can be fabricated according to the invention, resulting in efficient heat dissipation. The present invention also provides an inductive-resistive fluorescent apparatus which can be operated from DC battery power and which can be utilized for direct xe2x80x9cplug-inxe2x80x9d replacement of incandescent bulbs.
The invention further provides a method of inducing fluorescence via electromagnetic field interaction between an inductive-resistive structure and a fluorescent lamp. The method can be carried out using reliable, compact, lightweight and inexpensive hardware according to the present invention.
Still another method of the present invention includes delaying the application of the electrical potential to the fluorescent lamp for a first time period until the electrical potential imposed on the fluorescent lamp causes the fluorescent lamp to heat to a first temperature. The electric potential is then imposed on the fluorescent lamp at a first level, and there is a delay for a second time period to allow the value of the rippled/pulsed direct current to stabilize. The value of the rippled/pulsed direct current is measured, and the electric potential is imposed on the fluorescent lamp at a second level. The value of the rippled/pulsed direct current is then measured again. The value of a dimming voltage is measured and the electric potential imposed on the fluorescent lamp is adjusted in response to the measured dimming voltage.
In still another aspect of the present invention, a fluorescent illuminating apparatus includes a source of rippled/pulsed direct current responsive to a control sub-circuit. The control sub-circuit outputs a lamp voltage signal representative of a value of the electric potential to be imposed on the fluorescent lamp. A power supply sub-circuit, is responsive to the control sub-circuit, and the power supply sub-circuit imposes the electric potential on the fluorescent lamp at the value represented by the lamp voltage signal.
For a better understanding of the present invention, together with other and further objects and advantages, reference is made to the following description, taken in conjunction with the accompanying drawings, and its scope will be pointed out in the appended claims.